Predicting coral bleaching in Kimbe Bay

Sea surface temperatures monitored via satellite by NOAA rise, sending a Conservancy scientist and her team underwater for a rapid reef survey. Find out what they found and what could happen in the coming months.

KIMBE BAY: Snorkelling over a shallow coral reef off Restoff Island in Kimbe Bay, West New Britain, Papua New Guinea. This area is one of the Marine Protected Areas (MPAs) which The Nature Conservancy helped design to protect the biodiversity of the bay.

Last year, we helped NOAA install a sea-surface temperature (SST) buoy in Kimbe Bay to measure the actual SST in the water and beam the information back to NOAA via satellite — the first one in the Coral Triangle. NOAA has been using this information to validate the accuracy of their satellite-derived data, and so far both instruments are tracking very closely (i.e. showing the same temperature).

Recently, Mark Eakin of NOAA warned us that their monitoring devices indicated that the SST in Kimbe Bay had exceeded the bleaching threshold twice in two months (May and June), and that the reefs were at Bleaching Alert Level 1 (which means that some bleaching is expected within a few weeks).

In mid-July, the Kimbe team and I conducted a rapid survey of the reefs on the western side of Kimbe Bay with Walindi Plantation Resort. As NOAA had predicted, there was some coral bleaching in Kimbe Bay. Most of the bleached corals were from susceptible genera like branching and plate Acropora, with a few massive and mushroom corals also bleached. Bleaching was quite mild with 1-2% of corals bleached from 3-25m deep. There was more bleaching in shallow water (5-10%), but this was probably related to unusually low tides at the time.

This concentration of bleaching near the surface was despite the fact that the water temperature was 30oC down to 20m or more! That’s probably because Kimbe Bay is located in the Western Pacific Warm Pool – the warmest water in the world. While the water is pretty warm it is not that much warmer now than it usually is at this time of year, so most corals do not appear to be very stressed by the warm sea temperatures.

However, coral bleaching can develop over a number of weeks, and our Kimbe Bay team has implemented a Bleaching Watch Program to keep a close eye on the situation in Kimbe, and they will let us know if anything changes. Fortunately, water temperatures are dropping now and the threat of bleaching seems to have passed.

If we do get a major bleaching event in Kimbe, we will implement a rapid field assessment to identify areas that appear more resistant or resilient to coral bleaching. Our field teams will then work with local communities to ensure that these areas are included in the MPA network and protected from other threats.

NOAA’s near real time SST data for Kimbe Bay, showing that SSTs (purple line) exceeded the bleaching threshold (light blue line) twice in May and June, with a Bleaching Alert 1 issued in June. You can monitor this data for Kimbe Bay and other places atNOAA’s website. (Image: NOAA)